Preheat the oven to 175°C. Grease and flour baking trays or whoopie pie tins. Sift the flour, cocoa and baking soda together into a large bowl. Place the sugar and butter in to the bowl of an electric mixer and beat on a medium speed for 2 – 3 minutes or until light and creamy. Add the vanilla extract and egg and beat for a further minute. Reduce the speed and add the flour mixture in three batches, alternating with the milk. Beat until combined.

Place 1 ½ tablespoon amounts of batter about 5 cm apart of the trays and bake for 8 – 10 minutes or until they are cooked through. Cool for 5 minutes on the trays and then transfer to wire racks to cool completely.

To make the buttercream, place the eggwhite and sugar in the top of a double boiler over a medium heat and whisk for 3 – 4 minutes, or until warm and the sugar has dissolved and then remove from the heat. Using an electric beater, beat the mixture on a medium – high speed for 6 – 7 minutes or until glossy and stiff peaks form. Reduce the speed and add in the butter, one cube at a time, beating well after each addition. Continue to beat for 3 – 4 minutes. Combine the melted chocolate and cocoa. Add to the eggwhite mixture and beat to combine.

Using a knife, spread a large blob of buttercream over the flat side of half of the cookies and sandwich with the remaining cookies. Alternatively, you can transfer the buttercream mixture into a piping bag fitted with a 1cm plain nozzle and pipe 2 tablespoons of filling onto half of the cookies before sandwiching with the remaining cookies. Enjoy!

So, now that I have finally attempted these little cakey pies I am looking forward to trying out some different flavours; chocolate mint, black velvet, vanilla… I’ve even seen a recipe for spiced pumpkin whoopie pies with pecan mascarpone!

And, if you have been left with 3 egg yolks after making these, don’t worry – I have a very, very rich chocolate tart recipe on its way which will use them all up!

They are quite expensive (between $50-60)so an alternative is to draw circles onto baking paper and pipe on the mixture. I haven't looked, but the speciality cake tin places that hire their stock out might have them too.